FACTORS WHICH AFFECT THE RELEASE OF NEWCASTLE DISEASE AND SENDAI VIRUSES FROM INFECTED ALLANTOIC CELLS

Block to influenza virus replication in cells preirradiated with ultraviolet light

Ultraviolet (uv) irradiation of CEF cells immediately before infection with influenza A (fowl plague) virus inhibited virus growth; no inhibition of the growth of a parainfluenza virus (Newcastle disease virus) could be detected in irradiated cells. The kinetics of inhibition after various doses of uv irradiation were multihit, with an extrapolation number of two. When irradiated cells were allowed to photoreactivate by exposure to visible light for 16 hr their capacity to support influenza virus replication was largely restored; this process was sensitive to caffeine, suggesting that it required DNA repair. In CEF cells exposed to 360 ergs/mm(2) of uv radiation the rate of synthesis of host cellular RNA was reduced by more than 90%, and that of host cellular protein by 40-50%, as judged by incorporation of precursor molecules into an acid-insoluble form. When such irradiated cells were infected with influenza virus all the genome RNA segments were transcribed, but the overall concentration of virus-specific poly (A)-containing cRNA was reduced about 50-fold. Within this population of cRNA molecules, the RNAs coding for late proteins (HA, NA, and M) were reduced in amount relative to the other segments. The rates of synthesis of the M and HA proteins were specifically reduced in uv-irradiated cells, but the rates of synthesis of the P, NP, and NS proteins were only slightly reduced compared to normal cells. Immunofluorescent studies showed that, in uv-irradiated cells, NP migrated into the nucleus early after infection and later migrated out into the cytoplasm, as in normal cells. In contrast to normal cells, no specific immunofluorescence associated with M protein could be observed in uv-irradiated cells. It is concluded that uv-induced damage to host cellular DNA alters the pattern of RNA transcription in CEF cells infected with influenza virus, and that this results in a block to late protein synthesis which stops virus production.

Dependence of virus adsorption to the cell surface on the input multiplicity of infection

A state of "saturation" of the cell surface ensues when only 5-10% of the cell surface is "covered" by the adsorbed virions. Hence, this state cannot be explained by an "overcrowding effect" caused by the virions attached to the cell surface. A hypothesis of heterogeneity of the cell surface with regard to the virus absorbtion ("the domain hypothesis") is suitable for explanation.

Cell receptors for paramyxoviruses

Treatment of chick embryo fibroblasts, calf kidney and BHK cells for 30 minutes with the enzyme neuraminidase from Vibrio cholerae causes an enhancement of the per cent of attached NDV virions. This enhancement does not depend on the multiplicity of infection. The quantity of spontaneously eluted and cellbound virus is two times greater than the quantity of the same virus derived from control cells. N-acetyl-neuramin lactose inhibits the effect of Vibrio cholerae neuraminidase. After prolonged action of this enzyme, the quantity of adsorbed NDV diminishes. Treatment of the same cells with neuraminidase from influenza virus decreases the per cent of adsorbed NDV with respect to controls. The other paramyxovirus--bovine parainfluenza 3 virus adsorbs also more intensively on cells treated with Vibrio cholerae neuraminidase. It is suggested that partial hydrolysis of NANA molecules causes a rearrangement of the cell surface charged groups and thus allows a more effective contact between paramyxoviruses and the cell.

Ribonucleic acid polymerase induced in cells infected with Sendai virus

A ribonucleic acid (RNA)-dependent RNA polymerase was induced in chick embryo fibroblast cells after infection with Sendai virus (parainfluenza 1 virus). The enzyme was associated with the microsomal fraction of infected cells and reached maximum detectable activity at 18 hr after virus infection. The activity of the enzyme in vitro was dependent on the presence of added magnesium ions and all four nucleoside triphosphates and was not inhibited by actinomycin D. The RNA synthesized by the enzyme in vitro was sensitive to ribonuclease and consisted of a complex mixture of RNA species including 34S, 24S, and 18S components. Similar RNA components were detected in the microsomal fraction of Sendai virus-infected cells by labeling with (3)H-uridine from 17 to 18 hr postinfection in the presence of actinomycin D. Of the RNA synthesized by Sendai virus-induced RNA polymerase in vitro, 98% became insensitive to ribonuclease after annealing with RNA extracted from purified Sendai virus particles.